Methods and apparatus for multiple user uplink

ABSTRACT

Methods and apparatus for multiple user uplink are provided. In one aspect, a method for wireless communication is provided. The method includes transmitting a clear to transmit (CTX) message to two or more stations, the CTX indicating an uplink transmission opportunity, the CTX message further comprising a request that the two or more stations concurrently transmit uplink data at a specific time. The method further includes receiving a plurality of uplink data from at least two stations at the specific time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 61/871,269 entitled “METHODS ANDAPPARATUS FOR MULTIPLE USER UPLINK” filed on Aug. 28, 2013 thedisclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND

1. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications, and more particularly, to methods and apparatus formultiple user uplink communication in a wireless network.

2. Background

In many telecommunication systems, communications networks are used toexchange messages among several interacting spatially-separated devices.Networks may be classified according to geographic scope, which couldbe, for example, a metropolitan area, a local area, or a personal area.Such networks may be designated respectively as a wide area network(WAN), metropolitan area network (MAN), local area network (LAN), orpersonal area network (PAN). Networks also differ according to theswitching/routing technique used to interconnect the various networknodes and devices (e.g., circuit switching vs. packet switching), thetype of physical media employed for transmission (e.g., wired vs.wireless), and the set of communication protocols used (e.g., Internetprotocol suite, SONET (Synchronous Optical Networking), Ethernet, etc.).

Wireless networks are often preferred when the network elements aremobile and thus have dynamic connectivity needs, or if the networkarchitecture is formed in an ad hoc, rather than fixed, topology.Wireless networks employ intangible physical media in an unguidedpropagation mode using electromagnetic waves in the radio, microwave,infrared, optical, etc. frequency bands. Wireless networksadvantageously facilitate user mobility and rapid field deployment whencompared to fixed wired networks.

In order to address the issue of increasing bandwidth requirements thatare demanded for wireless communications systems, different schemes arebeing developed to allow multiple user terminals to communicate with asingle access point by sharing the channel resources while achievinghigh data throughputs. With limited communication resources, it isdesirable to reduce the amount of traffic passing between the accesspoint and the multiple terminals. For example, when multiple terminalssend uplink communications to the access point, it is desirable tominimize the amount of traffic to complete the uplink of alltransmissions. Thus, there is a need for an improved protocol for uplinktransmissions from multiple terminals.

SUMMARY

Various implementations of systems, methods and devices within the scopeof the appended claims each have several aspects, no single one of whichis solely responsible for the desirable attributes described herein.Without limiting the scope of the appended claims, some prominentfeatures are described herein.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

One aspect of the disclosure provides a method of wirelesscommunication. The method comprises transmitting a clear to transmit(CTX) message to two or more stations, the CTX message indicating anuplink transmission opportunity, the CTX message further comprising arequest that the two or more stations concurrently transmit uplink dataat a specific time. The method further comprises receiving a pluralityof uplink data transmissions from at least two stations at the specifictime.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus comprising a transmitter configured totransmit a clear to transmit (CTX) message to two or more stations, theCTX message indicating an uplink transmission opportunity, the CTXmessage further comprising a request that the two or more stationsconcurrently transmit uplink data at a specific time. The apparatusfurther comprising a receiver configured to receive a plurality ofuplink data transmissions from at least two stations at the specifictime.

Another aspect of the disclosure provides an apparatus for wirelesscommunication. The apparatus comprising means for transmitting a clearto transmit (CTX) message to two or more stations, the CTX messageindicating an uplink transmission opportunity, the CTX message furthercomprising a request that the two or more stations concurrently transmituplink data at a specific time. The apparatus further comprising meansfor receiving a plurality of uplink data transmissions from at least twostations at the specific time.

Another aspect of the disclosure provides a non-transitory computerreadable medium. The medium comprising instructions that when executedcause a processor to perform a method of transmitting a clear totransmit (CTX) message to two or more stations, the CTX messageindicating an uplink transmission opportunity, the CTX message furthercomprising a request that the two or more stations concurrently transmituplink data at a specific time. The medium further comprisinginstructions that when executed cause a processor to perform a method ofreceiving a plurality of uplink data transmissions from at least twostations at the specific time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a multiple-access multiple-input multiple-output(MIMO) system with access points and user terminals.

FIG. 2 illustrates a block diagram of the access point 110 and two userterminals 120 m and 120 x in a MIMO system.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice that may be employed within a wireless communication system.

FIG. 4A shows a time diagram of an example frame exchange of an uplink(UL) MU-MIMO communication.

FIG. 4B shows a time diagram of an example frame exchange of an uplink(UL) MU-MIMO communication.

FIG. 5 shows a time diagram of another example frame exchange of anUL-MU-MIMO communication.

FIG. 6 shows a time diagram of another example frame exchange of anUL-MU-MIMO communication.

FIG. 7 shows a time diagram of another example frame exchange of anUL-MU-MIMO communication.

FIG. 8 is a message timing diagram of one embodiment of multi-useruplink communication.

FIG. 9 shows a diagram of one embodiment of a request to transmit (RTX)frame.

FIG. 10 shows a diagram of one embodiment of a clear to transmit (CTX)frame.

FIG. 11 shows a diagram of another embodiment of a CTX frame.

FIG. 12 shows a diagram of another embodiment of a CTX frame.

FIG. 13 shows a diagram of another embodiment of a CTX frame.

FIG. 14 is a flow chart of an aspect of an exemplary method forproviding wireless communication.

DETAILED DESCRIPTION

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. The teachings disclosure may, however, be embodied in manydifferent forms and should not be construed as limited to any specificstructure or function presented throughout this disclosure. Rather,these aspects are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the disclosure to thoseskilled in the art. Based on the teachings herein one skilled in the artshould appreciate that the scope of the disclosure is intended to coverany aspect of the novel systems, apparatuses, and methods disclosedherein, whether implemented independently of or combined with any otheraspect of the invention. For example, an apparatus may be implemented ora method may be practiced using any number of the aspects set forthherein. In addition, the scope of the invention is intended to coversuch an apparatus or method which is practiced using other structure,functionality, or structure and functionality in addition to or otherthan the various aspects of the invention set forth herein. It should beunderstood that any aspect disclosed herein may be embodied by one ormore elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

Wireless network technologies may include various types of wirelesslocal area networks (WLANs). A WLAN may be used to interconnect nearbydevices together, employing widely used networking protocols. Thevarious aspects described herein may apply to any communicationstandard, such as Wi-Fi or, more generally, any member of the IEEE802.11 family of wireless protocols.

In some aspects, wireless signals may be transmitted according to ahigh-efficiency 802.11 protocol using orthogonal frequency-divisionmultiplexing (OFDM), direct-sequence spread spectrum (DSSS)communications, a combination of OFDM and DSSS communications, or otherschemes. Implementations of the high-efficiency 802.11 protocol may beused for Internet access, sensors, metering, smart grid networks, orother wireless applications. Advantageously, aspects of certain devicesimplementing this particular wireless protocol may consume less powerthan devices implementing other wireless protocols, may be used totransmit wireless signals across short distances, and/or may be able totransmit signals less likely to be blocked by objects, such as humans.

In some implementations, a WLAN includes various devices which are thecomponents that access the wireless network. For example, there may betwo types of devices: access points (“APs”) and clients (also referredto as stations, or “STAs”). In general, an AP serves as a hub or basestation for the WLAN and an STA serves as a user of the WLAN. Forexample, a STA may be a laptop computer, a personal digital assistant(PDA), a mobile phone, etc. In an example, an STA connects to an AP viaa Wi-Fi (e.g., IEEE 802.11 protocol such as 802.11ah) compliant wirelesslink to obtain general connectivity to the Internet or to other widearea networks. In some implementations an STA may also be used as an AP.

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Spatial Division Multiple Access (SDMA),Time Division Multiple Access (TDMA), Orthogonal Frequency DivisionMultiple Access (OFDMA) systems, Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) systems, and so forth. An SDMA system mayutilize sufficiently different directions to simultaneously transmitdata belonging to multiple user terminals. A TDMA system may allowmultiple user terminals to share the same frequency channel by dividingthe transmission signal into different time slots, each time slot beingassigned to different user terminal. A TDMA system may implement GSM orsome other standards known in the art. An OFDMA system utilizesorthogonal frequency division multiplexing (OFDM), which is a modulationtechnique that partitions the overall system bandwidth into multipleorthogonal sub-carriers. These sub-carriers may also be called tones,bins, etc. With OFDM, each sub-carrier may be independently modulatedwith data. An OFDM system may implement IEEE 802.11 or some otherstandards known in the art. An SC-FDMA system may utilize interleavedFDMA (IFDMA) to transmit on sub-carriers that are distributed across thesystem bandwidth, localized FDMA (LFDMA) to transmit on a block ofadjacent sub-carriers, or enhanced FDMA (EFDMA) to transmit on multipleblocks of adjacent sub-carriers. In general, modulation symbols are sentin the frequency domain with OFDM and in the time domain with SC-FDMA. ASC-FDMA system may implement 3GPP-LTE (3rd Generation. PartnershipProject Long Term Evolution) or other standards.

The teachings herein may be incorporated into (e.g., implemented withinor performed by) a variety of wired or wireless apparatuses (e.g.,nodes). In some aspects, a wireless node implemented in accordance withthe teachings herein may comprise an access point or an access terminal.

An access point (“AP”) may comprise, be implemented as, or known as aNodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller(“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”),Transceiver Function (“TF”), Radio Router, Radio Transceiver, BasicService Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station(“RBS”), or some other terminology.

A station “STA” may also comprise, be implemented as, or known as a userterminal, an access terminal (“AT”), a subscriber station, a subscriberunit, a mobile station, a remote station, a remote terminal, a useragent, a user device, user equipment, or some other terminology. In someimplementations an access terminal may comprise a cellular telephone, acordless telephone, a Session Initiation Protocol (“SIP”) phone, awireless local loop (“WLL”) station, a personal digital assistant(“PDA”), a handheld device having wireless connection capability, orsome other suitable processing device connected to a wireless modem.Accordingly, one or more aspects taught herein may be incorporated intoa phone (e.g., a cellular phone or smartphone), a computer (e.g., alaptop), a portable communication device, a headset, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music or video device, or a satellite radio), a gamingdevice or system, a global positioning system device, or any othersuitable device that is configured to communicate via a wireless medium.

FIG. 1 is a diagram that illustrates a multiple-access multiple-inputmultiple-output (MIMO) system 100 with access points and user terminals.For simplicity, only one access point 110 is shown in FIG. 1. An accesspoint is generally a fixed station that communicates with the userterminals and may also be referred to as a base station or using someother terminology. A user terminal or STA may be fixed or mobile and mayalso be referred to as a mobile station or a wireless device, or usingsome other terminology. The access point 110 may communicate with one ormore user terminals 120 at any given moment on the downlink and uplink.The downlink (i.e., forward link) is the communication link from theaccess point to the user terminals, and the uplink (i.e., reverse link)is the communication link from the user terminals to the access point. Auser terminal may also communicate peer-to-peer with another userterminal. A system controller 130 couples to and provides coordinationand control for the access points.

While portions of the following disclosure will describe user terminals120 capable of communicating via Spatial Division Multiple Access(SDMA), for certain aspects, the user terminals 120 may also includesome user terminals that do not support SDMA. Thus, for such aspects,the AP 110 may be configured to communicate with both SDMA and non-SDMAuser terminals. This approach may conveniently allow older versions ofuser terminals (“legacy” stations) that do not support SDMA to remaindeployed in an enterprise, extending their useful lifetime, whileallowing newer SDMA user terminals to be introduced as deemedappropriate.

The system 100 employs multiple transmit and multiple receive antennasfor data transmission on the downlink and uplink. The access point 110is equipped with N_(ap) antennas and represents the multiple-input (MI)for downlink transmissions and the multiple-output (MO) for uplinktransmissions. A set of K selected user terminals 120 collectivelyrepresents the multiple-output for downlink transmissions and themultiple-input for uplink transmissions. For pure SDMA, it is desired tohave N_(ap)≦K≦1 if the data symbol streams for the K user terminals arenot multiplexed in code, frequency or time by some means. K may begreater than N_(ap) if the data symbol streams can be multiplexed usingTDMA technique, different code channels with CDMA, disjoint sets ofsub-bands with OFDM, and so on. Each selected user terminal may transmituser-specific data to and/or receive user-specific data from the accesspoint. In general, each selected user terminal may be equipped with oneor multiple antennas (i.e., N_(ut)≧1). The K selected user terminals canhave the same number of antennas, or one or more user terminals may havea different number of antennas.

The SDMA system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. The MIMO system 100may also utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported). The system 100 may also be a TDMA system if theuser terminals 120 share the same frequency channel by dividingtransmission/reception into different time slots, where each time slotmay be assigned to a different user terminal 120.

FIG. 2 illustrates a block diagram of the access point 110 and two userterminals 120 m and 120 x in MIMO system 100. The access point 110 isequipped with N_(t) antennas 224 a through 224 ap. The user terminal 120m is equipped with N_(ut), antennas 252 _(ma) through 252 _(mu), and theuser terminal 120 x is equipped with N_(ut,x) antennas 252 _(xa) through252 _(xu). The access point 110 is a transmitting entity for thedownlink and a receiving entity for the uplink. The user terminal 120 isa transmitting entity for the uplink and a receiving entity for thedownlink. As used herein, a “transmitting entity” is an independentlyoperated apparatus or device capable of transmitting data via a wirelesschannel, and a “receiving entity” is an independently operated apparatusor device capable of receiving data via a wireless channel. In thefollowing description, the subscript “dn” denotes the downlink, thesubscript “up” denotes the uplink, N_(up) user terminals are selectedfor simultaneous transmission on the uplink, and N_(up) user terminalsare selected for simultaneous transmission on the downlink. N_(up) mayor may not be equal to N_(dn), and N_(up) and N_(dn) may be staticvalues or may change for each scheduling interval. Beam-steering or someother spatial processing technique may be used at the access point 110and/or the user terminal 120.

On the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. The TX data processor288 processes (e.g., encodes, interleaves, and modulates) the trafficdata for the user terminal based on the coding and modulation schemesassociated with the rate selected for the user terminal and provides adata symbol stream. A TX spatial processor 290 performs spatialprocessing on the data symbol stream and provides N_(ut,m) transmitsymbol streams for the N_(ut,m) antennas. Each transmitter unit (TMTR)254 receives and processes (e.g., converts to analog, amplifies,filters, and frequency upconverts) a respective transmit symbol streamto generate an uplink signal. N_(ut,m) transmitter units 254 provideN_(ut,m) uplink signals for transmission from N_(ut,m) antennas 252, forexample to transmit to the access point 110.

N_(up) user terminals may be scheduled for simultaneous transmission onthe uplink. Each of these user terminals may perform spatial processingon its respective data symbol stream and transmit its respective set oftransmit symbol streams on the uplink to the access point 110.

At the access point 110, N_(up) antennas 224 a through 224 _(ap) receivethe uplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(up) received symbol streams from N_(up)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing may be performed in accordancewith the channel correlation matrix inversion (CCMI), minimum meansquare error (MMSE), soft interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream is an estimate of adata symbol stream transmitted by a respective user terminal. An RX dataprocessor 242 processes (e.g., demodulates, deinterleaves, and decodes)each recovered uplink data symbol stream in accordance with the rateused for that stream to obtain decoded data. The decoded data for eachuser terminal may be provided to a data sink 244 for storage and/or acontroller 230 for further processing.

On the downlink, at the access point 110, a TX data processor 210receives traffic data from a data source 208 for N_(dn) user terminalsscheduled for downlink transmission, control data from a controller 230,and possibly other data from a scheduler 234. The various types of datamay be sent on different transport channels. TX data processor 210processes (e.g., encodes, interleaves, and modulates) the traffic datafor each user terminal based on the rate selected for that userterminal. The TX data processor 210 provides N_(dn) downlink data symbolstreams for the N_(dn) user terminals. A TX spatial processor 220performs spatial processing (such as a precoding or beamforming) on theN_(dn) downlink data symbol streams, and provides N_(up) transmit symbolstreams for the N_(up) antennas. Each transmitter unit 222 receives andprocesses a respective transmit symbol stream to generate a downlinksignal. N_(up) transmitter units 222 may provide N_(up) downlink signalsfor transmission from N_(up) antennas 224, for example to transmit tothe user terminals 120.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ut,m)downlink signals from the access point 110. Each receiver unit 254processes a received signal from an associated antenna 252 and providesa received symbol stream. An RX spatial processor 260 performs receiverspatial processing on N_(ut,m) received symbol streams from N_(ut,m)receiver units 254 and provides a recovered downlink data symbol streamfor the user terminal 120. The receiver spatial processing may beperformed in accordance with the CCMI, MMSE, or some other technique. AnRX data processor 270 processes (e.g., demodulates, deinterleaves anddecodes) the recovered downlink data symbol stream to obtain decodeddata for the user terminal.

At each user terminal 120, a channel estimator 278 estimates thedownlink channel response and provides downlink channel estimates, whichmay include channel gain estimates, SNR estimates, noise variance and soon. Similarly, a channel estimator 228 estimates the uplink channelresponse and provides uplink channel estimates. Controller 280 for eachuser terminal typically derives the spatial filter matrix for the userterminal based on the downlink channel response matrix H_(dn,m) for thatuser terminal. Controller 230 derives the spatial filter matrix for theaccess point based on the effective uplink channel response matrixH_(up,eff). The controller 280 for each user terminal may send feedbackinformation (e.g., the downlink and/or uplink eigenvectors, eigenvalues,SNR estimates, and so on) to the access point 110. The controllers 230and 280 may also control the operation of various processing units atthe access point 110 and user terminal 120, respectively.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the wireless communication system100. The wireless device 302 is an example of a device that may beconfigured to implement the various methods described herein. Thewireless device 302 may implement an access point 110 or a user terminal120.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 may perform logical and arithmetic operations based onprogram instructions stored within the memory 306. The instructions inthe memory 306 may be executable to implement the methods describedherein.

The processor 304 may comprise or be a component of a processing systemimplemented with one or more processors. The one or more processors maybe implemented with any combination of general-purpose microprocessors,microcontrollers, digital signal processors (DSPs), field programmablegate array (FPGAs), programmable logic devices (PLDs), controllers,state machines, gated logic, discrete hardware components, dedicatedhardware finite state machines, or any other suitable entities that canperform calculations or other manipulations of information.

The processing system may also include machine-readable media forstoring software. Software shall be construed broadly to mean any typeof instructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (e.g., in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the one or more processors, cause theprocessing system to perform the various functions described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A single or a plurality of transceiver antennas 316 may be attached tothe housing 308 and electrically coupled to the transceiver 314. Thewireless device 302 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

Certain aspects of the present disclosure support transmitting an uplink(UL) signal from multiple STAs to an AP. In some embodiments, the ULsignal may be transmitted in a multi-user MIMO (MU-MIMO) system.Alternatively, the UL signal may be transmitted in a multi-user FDMA(MU-FDMA) or similar FDMA system. Specifically, FIGS. 4-8, and 10illustrate UL-MU-MIMO transmissions 410A, 410B, 1050A, and 1050B thatwould apply equally to UL-FDMA transmissions. In these embodiments,UL-MU-MIMO or UL-FDMA transmissions can be sent simultaneously frommultiple STAs to an AP and may create efficiencies in wirelesscommunication.

An increasing number of wireless and mobile devices put increasingstress on bandwidth requirements that are demanded for wirelesscommunications systems. With limited communication resources, it isdesirable to reduce the amount of traffic passing between the AP and themultiple STAs. For example, when multiple terminals send uplinkcommunications to the access point, it is desirable to minimize theamount of traffic to complete the uplink of all transmissions. Thus,embodiments described herein support utilizing communication exchanges,scheduling and certain frames for increasing throughput of uplinktransmissions to the AP.

FIG. 4A is a time sequence diagram illustrating an example of anUL-MU-MIMO protocol 400 that may be used for UL communications. As shownin FIG. 4A and in conjunction with FIG. 1, the AP 110 may transmit aclear to transmit (CTX) message 402 to the user terminals 120 indicatingwhich STAs may participate in the UL-MU-MIMO scheme, such that aparticular STA knows to start an UL-MU-MIMO. In some embodiments, theCTX message may be transmitted in a payload portion of a physical layerconvergence protocol (PLCP) protocol data units (PPDUs). An example of aCTX frame structure is described more fully below with reference toFIGS. 12-15.

Once a user terminal 120 receives a CTX message 402 from the AP 110where the user terminal is listed, the user terminal may transmit theUL-MU-MIMO transmission 410. In FIG. 4A, STA 120A and STA 120B transmitUL-MU-MIMO transmission 410A and 410B containing physical layerconvergence protocol (PLCP) protocol data units (PPDUs). Upon receivingthe UL-MU-MIMO transmission 410, the AP 110 may transmit blockacknowledgments (BAs) 470 to the user terminals 120.

FIG. 4B is a time sequence diagram illustrating an example of anUL-MU-MIMO protocol that may be used for UL communications. In FIG. 4B,a CTX frame is aggregated in an A-MPDU message 407. The aggregatedA-MPDU message 407 may provide time to a user terminal 120 forprocessing before transmitting the UL signals or may allow the AP 110 tosend data to the user terminals 120 s before receiving uplink data.

Not all APs or user terminals 120 may support UL-MU-MIMO or UL-FDMAoperation. A capability indication from a user terminal 120 may beindicated in a high efficiency wireless (HEW) capability element that isincluded in an association request or probe request and may include abit indicating capability, the maximum number of spatial streams a userterminal 120 can use in a UL-MU-MIMO transmission, the frequencies auser terminal 120 can use in a UL-FDMA transmission, the minimum andmaximum power and granularity in the power backoff, and the minimum andmaximum time adjustment a user terminal 120 can perform.

A capability indication from an AP may be indicated in a HEW capabilityelement that is included in an association response, beacon or proberesponse and may include a bit indicating capability, the maximum numberof spatial streams a single user terminal 120 can use in a UL-MU-MIMOtransmission, the frequencies a single user terminal 120 can use in aUL-FDMA transmission, the required power control granularity, and therequired minimum and maximum time adjustment a user terminal 120 shouldbe able to perform.

In one embodiment, capable user terminals 120 may request to a capableAP to be part of the UL-MU-MIMO (or UL-FDMA) protocol by sending amanagement frame to AP indicating request for enablement of the use ofUL-MU-MIMO feature. In one aspect, an AP 110 may respond by granting theuse of the UL-MU-MIMO feature or denying it. Once the use of theUL-MU-MIMO is granted, the user terminal 120 may expect a CTX message402 at a variety of times. Additionally, once a user terminal 120 isenabled to operate the UL-MU-MIMO feature, the user terminal 120 may besubject to follow a certain operation mode. If multiple operation modesare possible, an AP may indicate to the user terminal 120 which mode touse in a HEW capability element, a management frame, or in an operationelement. In one aspect the user terminals 120 can change the operationmodes and parameters dynamically during operation by sending a differentoperating element to the AP 110. In another aspect the AP 110 may switchoperation modes dynamically during operation by sending an updatedoperating element or a management frame to a user terminal 120 or in abeacon. In another aspect, the operation modes may be indicated in thesetup phase and may be setup per user terminal 120 or for a group ofuser terminals 120. In another aspect the operation mode may bespecified per traffic identifier (TID).

FIG. 5 is a time sequence diagram that, in conjunction with FIG. 1,illustrates an example of an operation mode of a UL-MU-MIMOtransmission. In this embodiment, a user terminal 120 receives a CTXmessage 402 from an AP 110 and sends an immediate response to the AP110. The response may be in the form of a clear to send (CTS) 408 oranother similar signal. In one aspect, requirement to send a CTS may beindicated in the CTX message 402 or may be indicated in the setup phaseof the communication. As shown in FIG. 5, STA 120 A and STA 120B maytransmit a CTS 1 408A and CTS 2 408B message in response to receivingthe CTX message 402. The modulation and coding scheme (MCS) of the CTS 1408A and CTS 2 408B may be based on the MCS of the CTX message 402. Inthis embodiment, CTS 1 408A and CTS 2 408B contain the same bits and thesame scrambling sequence so that they may be transmitted to the AP 110at the same time. The duration field of the CTS 408 signals may be basedon the duration field in the CTX by removing the time for the CTX PPDU.The UL-MU-MIMO transmission 410A and 410B are then sent by the STAs 120Aand 120B as listed in the CTX 402 signals. The AP 110 may then sendacknowledgment (ACK) signals the STAs 120A and 120B. In some aspects,the ACK signals may be serial ACK signals to each station or BAs. Insome aspects the ACKs may be polled. This embodiment createsefficiencies by simultaneously transmitting CTS 408 signals frommultiple STAs to an AP 110 instead of sequentially, which saves time andreduces the possibility of interference.

FIG. 6 is a time sequence diagram that, in conjunction with FIG. 1,illustrates another example of an operation mode of a UL-MU-MIMOtransmission. In this embodiment, user terminals 120A and 120B receive aCTX message 402 from an AP 110 and are allowed to start and UL-MU-MIMOtransmission a time (T) 406 after the end of the PPDU carrying the CTXmessage 402. The T 406 may be a short interframe space (SIFS), pointinterframe space (PIFS), or another time potentially adjusted withadditional offsets as indicated by an AP 110 in the CTX message 402 orvia a management frame. The SIFS and PIFS time may be fixed in astandard or indicated by an AP 110 in the CTX message 402 or in amanagement frame. The benefit of T 406 may be to improve synchronizationor to allow a user terminals 120A and 120B time to process the CTXmessage 402 or other messages before transmission.

Referring to FIGS. 4-6, in conjunction with FIG. 1, the UL-MU-MIMOtransmission 410 may have a common duration. The duration of theUL-MU-MIMO transmission 410 for user terminals utilizing the UL-MU-MIMOfeature may be indicated in the CTX message 402 or during the setupphase. To generate a PPDU of the required duration, a user terminal 120may build a PLCP service data unit (PSDU) so that the length of the PPDUmatches the length indicated in the CTX message 402. In another aspect,a user terminal 120 may adjust the level of data aggregation in a mediaaccess control (MAC) protocol data unit (A-MPDU) or the level of dataaggregation in a MAC service data units (A-MSDU) to approach the targetlength. In another aspect, a user terminal 120 may add end of file (EOF)padding delimiters to reach the target length. In another approach thepadding or the EOF pad fields are added at the beginning of the A-MPDU.One of the benefits of having all the UL-MU-MIMO transmissions the samelength is that the power level of the transmission will remain constant.

In some embodiments, a user terminal 120 may have data to upload to theAP but the user terminal 120 has not received a CTX message 402 or othersignal indicating that the user terminal 120 may start a UL-MU-MIMOtransmission.

In one operation mode, the user terminals 120 may not transmit outsidean UL-MU-MIMO transmission opportunity (TXOP) (e.g., after CTX message402). In another operation mode user terminals 120 may transmit framesto initialize a UL-MU-MIMO transmission, and then may transmit duringthe UL-MU-MIMO TXOP, if for example, they are instructed to do so in aCTX message 402. In one embodiment, the frame to initialize a UL-MU-MIMOtransmission may be a request to transmit (RTX), a frame specificallydesigned for this purpose (an example of a RTX frame structure isdescribed more fully below with reference to FIGS. 8 and 9). The RTXframes may be the only frames a user terminal 120 is allowed to use toinitiate a UL MU MIMO TXOP. In one embodiment, the user terminal may nottransmit outside an UL-MU-MIMO TXOP other than by sending an RTX. Inanother embodiment, a frame to initialize an UL MU MIMO transmission maybe any frame which indicates to an AP 110 that a user terminal 120 hasdata to send. It may be pre-negotiated that these frames indicate a ULMU MIMO TXOP request. For example, the following may be used to indicatethat a user terminal 120 has data to send and is requesting an UL MUMIMO TXOP: an RTS, a data frame or QoS Null frame with bits 8-15 of theQoS control frame set to indicate more data, or a PS poll. In oneembodiment, the user terminal may not transmit outside an UL MU MIMOTXOP other than by sending frames to trigger this TXOP, where this framemay be an RTS, PS poll, or QOS null. In another embodiment, the userterminal may send single user uplink data as usual, and may indicate arequest for a UL MU MIMO TXOP by setting bits in the QoS control frameof its data packet. FIG. 7 is a time sequence diagram illustrating, inconjunction with FIG. 1, an example where the frame to initialize aUL-MU-MIMO is a RTX 701. In this embodiment the user terminal 120 sendsto the AP 110 a RTX 701 that includes information regarding theUL-MU-MIMO transmission. As shown in FIG. 7, the AP 110 may respond tothe RTX 701 with a CTX message 402 granting an UL-MU-MIMO TXOP to sendthe UL-MU-MIMO transmission 410 immediately following the CTX message402. In another aspect, the AP 110 may respond with a CTS that grants asingle-user (SU) UL TXOP. In another aspect, the AP 110 may respond witha frame (e.g., ACK or CTX with a special indication) that acknowledgesthe reception of the RTX 701 but does not grant an immediate UL-MU-MIMOTXOP. In another aspect, the AP 110 may respond with a frame thatacknowledges the reception of the RTX 701, does not grant an immediateUL-MU-MIMO TXOP, but grants a delayed UL-MU-MIMO TXOP and may identifythe time of the TXOP is granted. In this embodiment, the AP 110 may senda CTX message 402 to start the UL-MU-MIMO at the granted time.

In another aspect, the AP 110 may respond to the RTX 701 with an ACK orother response signal which does not grant the user terminal 120 anUL-MU-MIMO transmission but indicates that the user terminal 120 shallwait for a time (T) before attempting another transmission (e.g.,sending another RTX). In this aspect the time (T) may be indicated bythe AP 110 in the setup phase or in the response signal. In anotheraspect an AP 110 and a user terminal 120 may agree on a time which theuser terminal 120 may transmit a RTX 701, RTS, PS-poll, or any otherrequest for a UL-MU-MIMO TXOP.

In another operation mode, user terminals 120 may transmit requests forUL-MU-MIMO transmissions 410 in accordance with regular contentionprotocol. In another aspect, the contention parameters for userterminals 120 using UL-MU-MIMO are set to a different value than forother user terminals that are not using the UL-MU-MIMO feature. In thisembodiment, the AP 110 may indicate the value of the contentionparameters in a beacon, association response or through a managementframe. In another aspect, the AP 110 may provide a delay timer thatprevents a user terminal 120 from transmitting for a certain amount oftime after each successful UL-MU-MIMO TXOP or after each RTX, RTS,PS-poll, or QoS null frame. The timer may be restarted after eachsuccessful UL-MU-MIMO TXOP. In one aspect, the AP 110 may indicate thedelay timer to user terminals 120 in the setup phase or the delay timermay be different for each user terminal 120. In another aspect, the AP110 may indicate the delay timer in the CTX message 402 or the delaytimer may be dependent on the order of the user terminals 120 in the CTXmessage 402, and may be different for each terminal.

In another operational mode, the AP 110 may indicate a time intervalduring which the user terminals 120 are allowed to transmit a UL-MU-MIMOtransmission. In one aspect, the AP 110 indicates a time interval to theuser terminals 120 during which the user terminals are allowed to send aRTX or RTS or other request to the AP 110 to ask for an UL-MU-MIMOtransmission. In this aspect, the user terminals 120 may use regularcontention protocol. In another aspect, the user terminals may notinitiate a UL-MU-MIMO transmission during the time interval but the AP110 may send a CTX or other message to the user terminals to initiatethe UL-MU-MIMO transmission.

In certain embodiments, a user terminal 120 enabled for UL-MU-MIMO mayindicate to an AP 110 that it requests an UL-MU-MIMO TXOP because it hasdata pending for UL. In one aspect, the user terminal 120 may send a RTSor a PS-poll to request a UL-MU-MIMO TXOP. In another embodiment, theuser terminal 120 may send any data frame, including a quality ofservice (QoS) null data frame, where the bits 8-15 of the QoS controlfield indicate a non-empty queue. In this embodiment the user terminal120 may determine during the setup phase which data frames (e.g., RTS,PS-poll, QoS null, etc.) will trigger a UL-MU-MIMO transmission when thebits 8-15 of the QoS control field indicate a non-empty queue. In oneembodiment, the RTS, PS-poll, or QoS null frames may include a 1 bitindication allowing or disallowing the AP 110 to respond with a CTXmessage 402. In another embodiment, the QoS null frame may include TXpower information and a per TID queue information. The TX powerinformation and per TID queue information may be inserted in the twobytes of the sequence control and QoS controls fields in a QoS nullframe and the modified QoS null frame may be sent to the AP 110 torequest a UL-MU-MIMO TXOP. In another embodiment, referring to FIGS. 1and 7, the user terminal 120 may send a RTX 701 to request a UL-MU-MIMOTXOP.

In response to receiving an RTS, RTX, PS-poll or QoS null frame, orother trigger frame as described above, an AP 110 may send a CTX message402. In one embodiment, referring to FIG. 7, after the transmission ofthe CTX message 402 and the completion of the UL-MU-MIMO transmissions410A and 410B, TXOP returns to the STAs 120A and 120B which can decideon how to use the remaining TXOP. In another embodiment, referring toFIG. 7, after the transmission of the CTX message 402 and the completionof the UL-MU-MIMO transmissions 410A and 410B, TXOP remains with the AP110 and the AP 110 may use the remaining TXOP for additional UL-MU-MIMOtransmissions by sending another CTX message 402 to either STAs 120A and120B or to other STAs.

FIG. 8 is a message timing diagram of one embodiment of multi-useruplink communication. Message exchange 800 shows communication ofwireless messages between an AP 110 and three stations 120 a-c. Messageexchange 800 indicates that each of STAs 120 a-c transmits arequest-to-transmit (RTX) message 802 a-c to the AP 110. Each of RTXmessages 802 a-c indicate that the transmitting station 120 a-c has dataavailable to be transmitted to the AP 110.

After receiving each of RTX messages 802 a-c, the AP 110 may respondwith a message indicating that the AP 110 has received the RTX. As shownin FIG. 8, the AP 110 transmits ACK messages 803 a-c in response to eachRTX messages 802 a-c. In some embodiments, the AP 110 may transmit amessage (e.g., a CTX message) indicating that each of the RTX messages802 a-c has been received but that the AP 110 has not granted atransmission opportunity for the stations 120 a-c to uplink data. InFIG. 8, after sending ACK message 803 c, the AP 110 transmits a CTXmessage 804. In some aspects, the CTX message 804 is transmitted to atleast the stations STA 120 a-c. In some aspects, the CTX message 804 isbroadcast. In some aspects, the CTX message 804 indicates which stationsare granted permission to transmit data to the AP 110 during atransmission opportunity. The starting time of the transmissionopportunity and its duration may be indicated in the CTX message 804 insome aspects. For example, the CTX message 804 may indicate that thestations STA 120 a-c should set their network allocation vectors to beconsistent with NAV 812.

At a time indicated by the CTX message 804, the three stations 120 a-ctransmit data 806 a-c to the AP 110. The data 806 a-c are transmitted atleast partially concurrently during the transmission opportunity. Thetransmissions of data 806 a-c may utilize uplink multi-user multipleinput, multiple output transmissions (UL-MU-MIMO) or uplink frequencydivision multiple access (UL-FDMA).

In some aspects, stations STAa-c may transmit pad data such thetransmissions of each station transmitting during a transmissionopportunity are of approximately equal duration. Message exchange 800shows STA 120 a transmitting pad data 808 a while STA 120 c transmitspad data 808 c. The transmission of pad data ensure that thetransmissions from each of the STAs 120 a-c complete at approximatelythe same time. This may provide for a more equalized transmission powerover the entire duration of the transmission, optimizing AP 110 receiverefficiencies.

After the AP 110 receives the data transmissions 806 a-c, the AP 110transmits acknowledgments 810 a-c to each of the stations 120 a-c. Insome aspects, the acknowledgments 810 a-c may be transmitted at leastpartially concurrently using either DL-MU-MIMO or DL-FDMA.

FIG. 9 is a diagram of one embodiment of a RTX frame 900. The RTX frame900 includes a frame control (FC) field 910, a duration field 915(optional), a transmitter address (TA)/allocation identifier (AID) field920, a receiver address (RA)/basic service set identifier (BSSID) field925, a TID field 930, an estimated transmission (TX) time field 950, anda TX power field 970. The FC field 910 indicates a control subtype or anextension subtype. The duration field 915 indicates to any receiver ofthe RTX frame 900 to set the network allocation vector (NAV). In oneaspect, the RTX frame 900 may not have a duration field 915. The TA/AIDfield 920 indicates the source address which can be an AID or a full MACaddress. The RA/BSSID field 925 indicates the RA or BSSID of the STAs toconcurrently transmit uplink data. In one aspect the RTX frame may notcontain a RA/BSSID field 925. The TID field 930 indicates the accesscategory (AC) for which the user has data. The Estimated TX time field950 indicates the time requested for the UL-TXOP and may be the timerequired for a user terminal 120 to send all the data in its buffer atthe current planned MCS. The TX power field 970 indicates the power atwhich the frame is being transmitted and can be used by the AP toestimate the link quality and adapt the power backoff indication in aCTX frame.

In some embodiments, before an UL-MU-MIMO communication can take place,an AP 110 may collect information from the user terminals 120 that mayparticipate in the UL-MU-MIMO communication. An AP 110 may optimize thecollection of information from the user terminals 120 by scheduling thetransmissions from the user terminals 120.

As discussed above, the CTX message 402 may be used in a variety ofcommunications. FIG. 10 is a diagram of an example of a CTX frame 1000structure. In this embodiment, the CTX frame 1000 is a control framethat includes a frame control (FC) field 1005, a duration field 1010, atransmitter address (TA) field 1015, a control (CTRL) field 1020, a PPDUduration field 1025, a STA information (info) field 1030, and a framecheck sequence (FCS) field 1080. The FC field 1005 indicates a controlsubtype or an extension subtype. The duration field 1010 indicates toany receiver of the CTX frame 1000 to set the network allocation vector(NAV). The TA field 1015 indicates the transmitter address or a BSSID.The CTRL field 1020 is a generic field that may include informationregarding the format of the remaining portion of the frame (e.g., thenumber of STA info fields and the presence or absence of any subfieldswithin a STA info field), indications for rate adaptation for the userterminals 100, indication of allowed TID, and indication that a CTS mustbe sent immediately following the CTX frame 1000. The indications forrate adaptation may include data rate information, such as a numberindicating how much the STA should lower their MCSs, compared to the MCSthe STA would have used in a single user transmission. The CTRL field1020 may also indicate if the CTX frame 1000 is being used for UL MUMIMO or for UL FDMA or both, indicating whether a Nss or Tone allocationfield is present in the STA Info field 1030.

Alternatively, the indication of whether the CTX is for UL MU MIMO orfor UL FDMA can be based on the value of the subtype. Note that UL MUMIMO and UL FDMA operations can be jointly performed by specifying to aSTA both the spatial streams to be used and the channel to be used, inwhich case both fields are present in the CTX; in this case, the Nssindication is referred to a specific tone allocation. The PPDU duration1025 field indicates the duration of the following UL-MU-MIMO PPDU thatthe user terminals 120 are allowed to send. The STA Info 1030 fieldcontains information regarding a particular STA and may include aper-STA (per user terminal 120) set of information (see STA Info 1 1030and STA Info N 1075). The STA Info 1030 field may include an AID or MACaddress field 1032 which identifies a STA, a number of spatial streamsfield (Nss) 1034 field which indicates the number of spatial streams aSTA may use (in an UL-MU-MIMO system), a Time Adjustment 1036 fieldwhich indicates a time that a STA should adjust its transmissioncompared to the reception of a trigger frame (the CTX, in this case), aPower Adjustment 1038 field which indicates a power backoff a STA shouldtake from a declared transmit power, a Tone Allocation 1040 field whichindicates the tones or frequencies a STA may use (in a UL-FDMA system),an Allowed TID 1042 field which indicates the allowable TID, an AllowedTX Mode 1044 field which indicates the allowed TX modes, a MCS 1046field which indicates the MCS the STA should use, and a TX start timefield 1048 which indicates a start time for the STA to transmit uplinkdata. In some embodiments, the allowed TX modes may include a short/longguard interval (GI) or cyclic prefix mode, a binary convolutional code(BCC)/low density parity check (LDPC) mode (generally, a coding mode),or a space-time block coding (STBC) mode.

In some embodiments, the STA info fields 1030-1075 may be excluded fromthe CTX frame 1000. In these embodiments, the CTX frame 1000 with themissing STA info fields may indicate to the user terminals 120 receivingthe CTX frame 1000 that a request message to uplink data (e.g., RTS, RTXor QoS Null) has been received but a transmission opportunity has notbeen granted. In some embodiments, the control field 1020 may includeinformation regarding the requested uplink. For example, the controlfield 1020 may include a waiting time before sending data or anotherrequest, a reason code for why the request was not granted, or otherparameters for controlling medium access from the user terminal 120. ACTX frame with missing STA info fields may also apply to CTX frames1100, 1200 and 1300 described below.

In some embodiments, a user terminal 120 receiving a CTX with a AllowedTID 1042 indication may be allowed to transmit data only of that TID,data of the same or higher TID, data of the same or lower TID, any data,or only data of that TID first, then if no data is available, data ofother TIDs. The FCS 1080 field indicates the carries an FCS value usedfor error detection of the CTX frame 1000.

FIG. 11 is a diagram of another example of a CTX frame 1100 structure.In this embodiment and in conjunction with FIG. 10, the STA Info 1030field does not contain the AID or MAC Address 1032 field and instead theCTX frame 1000 includes a group identifier (GID) 1026 field whichidentifies the STAs to concurrently transmit uplink data by a groupidentifier rather than an individual identifier. FIG. 12 is a diagram ofanother example of a CTX frame 1200 structure. In this embodiment and inconjunction with FIG. 11, the GID 1026 field is replaced with a RA 1014field which identifies a group of STAs through a multicast MAC address.

FIG. 13 is a diagram of an example of a CTX frame 1300 structure. Inthis embodiment, the CTX frame 1300 is a management frame that includesa Management MAC Header 1305 field, a Body 1310 field, and a FCS 1380field. The Body 1310 field includes an IE ID 1315 field which identifiesan information element (IE), a LEN 1320 field which indicates the lengthof the CTX frame 1300, a CTRL 1325 field which includes the sameinformation as the CTRL 1020 field, a PPDU Duration 1330 field whichindicates the duration of the following UL-MU-MIMO PPDU that the userterminals 120 are allowed to send, a STA Info 1 1335 field and a MCS1375 field which can indicate the MCS for all the STAs to use in thefollowing UL-MU-MIMO transmission, or an MCS backoff for all the STAs touse in the following UL-MU-MIMO transmission. The STA Info 1 1335 (alongwith STA Info N 1370) field represent a per STA field that includes AID1340 field which identifies a STA, a number of spatial streams field(Nss) 1342 field which indicates the number of spatial streams a STA mayuse (in an UL-MU-MIMO system), a Time Adjustment 1344 field whichindicates a time that a STA should adjust its transmission time comparedto the reception of a trigger frame (the CTX in this case), a PowerAdjustment 1348 field which indicates a power backoff a STA should takefrom a declared transmit power, a Tone Allocation 1348 field whichindicates the tones or frequencies a STA may use (in a UL-FDMA system),an Allowed TID 1350 field which indicates the allowable TID, and a TXstart time field 1048 which indicates a start time for the STA totransmit uplink data.

In one embodiment, the CTX frame 1000 or the CTX frame 1300 may beaggregated in an A-MPDU to provide time to a user terminal 120 forprocessing before transmitting the UL signals. In this embodiment,padding or data may be added after the CTX to allow a user terminal 120additional time to process the forthcoming packet. One benefit topadding a CTX frame may be to avoid possible contention issues for theUL signals from other user terminals 120, as compared to increasing theinterframe space (IFS) as described above. In one aspect, if the CTX isa management frame, additional padding information elements (IEs) may besent. In one aspect, if the CTX is aggregated in a A-MPDU, additionalA-MPDU padding delimiters may be included. Padding delimiters may EoFdelimiters (4 Bytes) or other padding delimiters. In another aspect, thepadding may be achieved by adding data, control or Management MPDPUs, aslong as they do not require to be processed within the IFS responsetime. The MPDUs may include an indication indicating to the receiverthat no immediate response is required and will not be required by anyof the following MPDUs. In another aspect, the user terminals 120 mayrequest to an AP 110 a minimum duration or padding for the CTX frame. Inanother embodiment, the padding may be achieved by adding PHY OFDMAsymbols, which may include undefined bits not carrying information, ormay include bit sequences that carry information, as long as they do notneed to be processed within the IFS time.

In some embodiments, an AP 110 may initiate a CTX transmission. In oneembodiment, an AP 110 may send a CTX message 402 in accordance withregular enhanced distribution channel access (EDCA) contention protocol.In another embodiment, an AP 110 may send a CTX message 402 at scheduledtimes. In this embodiment, the scheduled times may be indicated by theAP 110 to the user terminals 120 by using a restricted access window(RAW) indication in a beacon which indicates a time reserved for a groupof user terminals 120 to access the medium, a target wake time (TWT)agreement with each user terminal 120 which indicates to multiple userterminals 120 to be awake at the same time to take part in a UL-MU-MIMOtransmission, or information in other fields. Outside the RAW and TWT auser terminal 102 may be allowed to transmit any frame, or only a subsetof frames (e.g., non-data frames). It may also be forbidden to transmitcertain frames (e.g., it may be forbidden to transmit data frames). Theuser terminal 120 may also indicate that it is in sleep state. Oneadvantage to scheduling a CTX is that multiple user terminals 120 may beindicated a same TWT or RAW time and may receive a transmission from anAP 110.

FIG. 14 is a flow chart of an exemplary method 1400 for wirelesscommunication in accordance with certain embodiments described herein. Aperson having ordinary skill in the art will appreciate that the method1400 may be implemented by any suitable device and system.

In operation block 1405, the method 1400 includes transmitting a clearto transmit (CTX) message to two or more stations, the CTX messageindicating an uplink transmission opportunity, the CTX message furthercomprising a request that the two or more stations concurrently transmituplink data at a specific time. In operational block 1410, the method1400 further includes receiving a plurality of uplink data from at leasttwo stations at the specific time.

In some embodiments, an apparatus for wireless communication may performsome of the functions of method 1400. The apparatus comprises means fortransmitting a clear to transmit (CTX) message to two or more stations,the CTX message indicating an uplink transmission opportunity, the CTXmessage further comprising a request that the two or more stationsconcurrently transmit uplink data at a specific time. The apparatus mayfurther comprise means for receiving a plurality of uplink data from atleast two stations at the specific time.

A person/one having ordinary skill in the art would understand thatinformation and signals can be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that can bereferenced throughout the above description can be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

Various modifications to the implementations described in thisdisclosure can be readily apparent to those skilled in the art, and thegeneric principles defined herein can be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the disclosure is not intended to be limited to theimplementations shown herein, but is to be accorded the widest scopeconsistent with the claims, the principles and the novel featuresdisclosed herein. The word “exemplary” is used exclusively herein tomean “serving as an example, instance, or illustration.” Anyimplementation described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other implementations.

Certain features that are described in this specification in the contextof separate implementations also can be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also can be implemented inmultiple implementations separately or in any suitable sub-combination.Moreover, although features can be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination can be directed to asub-combination or variation of a sub-combination.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of perforniing the operations.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

In one or more aspects, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium.Computer-readable media includes both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage media may be anyavailable media that can be accessed by a computer. By way of example,and not limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium that can be used tocarry or store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Thus, in some aspects computer readable medium may comprisenon-transitory computer readable medium (e.g., tangible media). Inaddition, in some aspects computer readable medium may comprisetransitory computer readable medium (e.g., a signal). Combinations ofthe above should also be included within the scope of computer-readablemedia.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. An apparatus for wireless communicationcomprising: a transmitter configured to transmit a clear to transmit(CTX) message to two or more stations, the CTX message indicating anuplink transmission opportunity, the CTX message further comprising arequest for the two or more stations to concurrently transmit uplinkdata at a specific time; and a receiver configured to receive aplurality of uplink data transmissions at the specific time from atleast two stations of the two or more stations.
 2. The apparatus ofclaim 1, wherein the uplink transmission opportunity has a commonduration for each of the plurality of uplink data transmissions.
 3. Theapparatus of claim 1, wherein the specific time is communicated based ona short interframe space (SIFS) or a point interframe space (PIFS) timeafter the end of the transmission of the message.
 4. The apparatus ofclaim 1, wherein the receiver is further configured to receive aplurality of clear to send (CTS) messages with having a commonscrambling sequence at a time after the end of the transmission of theCTX message and before the receiving of the plurality of uplink data. 5.The apparatus of claim 1, wherein the CTX message comprises a physicallayer data unit (PPDU) duration field indicating a duration for thetransmission of the uplink data.
 6. The apparatus of claim 1, whereinthe CTX message comprises one or more station (STA) information fieldsfor a particular station.
 7. The apparatus of claim 6, wherein thestation (STA) information field comprises an indication of allowedtransmission modes.
 8. The apparatus of claim 7, wherein the indicationof allowed transmission modes comprises one or more of a short/longguard interval (GI) or cyclic prefix mode, a binary convolutional code(BCC)/low density parity check (LDPC) mode, and a space-time blockcoding (STBC) mode.
 9. The apparatus of claim 6, wherein the station(STA) information field comprises a tone allocation field indicating thetone and/or frequencies for transmission of uplink data using afrequency division multiple access (FDMA) system and/or an orthogonalFDMA system.
 10. The apparatus of claim 6, wherein the station (STA)information field comprises a transmission start time field indicating astart time for transmission of uplink data.
 11. The apparatus of claim6, wherein the station (STA) information field comprises one or more ofan address identifier field, a number and index of spatial streams, atime adjustment field, a power adjustment field, an allowed trafficidentifier field, and a modulation and coding scheme field.
 12. Theapparatus of claim 1, wherein the CTX message comprises a groupidentifier (GID) field indicating the two or more stations as a group ofstations to concurrently transmit uplink data at the specific time. 13.The apparatus of claim 1, wherein the CTX message comprises a receiveraddress (RA) field indicating a unicast or multicast address whichidentifies the two or more stations to concurrently transmit uplink dataat the specific time.
 14. The apparatus of claim 1, wherein the CTXmessage comprises a field indicating data rate information for the twoor more stations as a group of stations to concurrently transmit uplinkdata at the specific time.
 15. The apparatus of claim 1, wherein the CTXmessage comprises one or more of a frame control field, a transmitteraddress field, a duration field, and a basic service set identifier(BSSID) field.
 16. The apparatus of claim 1, wherein the CTX messagecomprises a management frame or a control frame.
 17. The apparatus ofclaim 1, wherein the receiver is further configured to receive a requestfor transmission of uplink data from the two or more stations.
 18. Theapparatus of claim 17, wherein the request to transmit uplink datacomprises a request to send (RTS) message, a request to transmit (RTX)message, a power save (PS) poll message, or a quality of service (QoS)null message.
 19. The apparatus of claim 17, wherein the transmitter isfurther configured to transmit a second CTX message in response to therequest for transmission of uplink data, the second CTX messageindicating the request for transmission of uplink data has been receivedbut excluding an indication of the uplink transmission opportunity. 20.The apparatus of claim 1, wherein the transmitter is further configuredto transmit the CTX message aggregated with a second message.
 21. Amethod for wireless communication, comprising: transmitting a clear totransmit (CTX) message to two or more stations, the CTX messageindicating an uplink transmission opportunity, the CTX message furthercomprising a request for the two or more stations to concurrentlytransmit uplink data at a specific time; and receiving a plurality ofuplink data transmissions at the specific time from at least twostations of the two or more stations.
 22. The method of claim 21,wherein the CTX message comprises a receiver address (RA) fieldindicating a unicast or multicast address which identifies the two ormore stations to concurrently transmit uplink data at the specific time,wherein the CTX message further comprises a station (STA) informationfield.
 23. The method of claim 21, wherein the station (STA) informationfield comprises one or more of an address identifier field, a number ofspatial streams field, a time adjustment field, a power adjustmentfield, an allowed traffic identifier field, and a modulation and codingscheme field.
 24. The method of claim 21, further comprisingtransmitting the CTX message aggregated with a second message.
 25. Anapparatus for wireless communication comprising: means for transmittinga clear to transmit (CTX) message to two or more stations, the CTXmessage indicating an uplink transmission opportunity, the CTX messagefurther comprising a request for the two or more stations toconcurrently transmit uplink data at a specific time; and means forreceiving a plurality of uplink data transmissions at the specific timefrom at least two stations of the two or more stations.
 26. Theapparatus of claim 25, wherein the CTX message comprises a physicallayer data unit (PPDU) duration field indicating the duration of theuplink data and wherein the CTX message further comprises a receiveraddress (RA) field indicating a unicast or multicast address whichidentifies the two or more stations to concurrently transmit uplink dataat the specific time.
 27. The apparatus of claim 25, wherein the CTXmessage comprises a station (STA) information field comprising one ormore of an address identifier field, a number of spatial streams field,a time adjustment field, a power adjustment field, an allowed trafficidentifier field, a modulation and coding scheme field, an indication ofallowed transmission modes, and a tone allocation field.
 28. Anon-transitory computer readable medium comprising instructions thatwhen executed cause a processor to perform a method of: transmitting aclear to transmit (CTX) message to two or more stations, the CTX messageindicating an uplink transmission opportunity, the CTX message furthercomprising a request for the two or more stations to concurrentlytransmit uplink data at a specific time; and receiving a plurality ofuplink data transmissions at the specific time from at least twostations of the two or more stations.
 29. The medium of claim 28,wherein the method further comprises receiving a plurality of clear tosend (CTS) messages with having a common scrambling sequence at a timeafter the end of the transmission of the CTX message and before thereceiving of the plurality of uplink data.
 30. The medium of claim 28,transmitting the CTX message comprises transmitting the CTX message inresponse to a request for transmission of uplink data.